1. Field of the Invention
The present invention relates to an electrical heating device, in particular for a motor vehicle, with a housing, which encloses a circulation chamber through which a medium can flow, in which heating ribs protrude, which are in thermally conducting contact with at least one PTC heating element, and with a control device provided in a constructional unit with at least one assembled conductor board, which is accommodated in a control housing.
2. Description of the Related Art
An electrical heating device of this nature is known from EP 1 872 986 A1 which originates from the applicant. This prior-art electrical heating device involves a type with a housing, which encloses a circulation chamber through which a medium can flow. In this respect the heating ribs protrude enveloped by heating ribs with in each case a U-shaped recess in the circulation chamber. The U-shaped recesses are provided within the housing and separate the circulation chamber, through which the fluid to be heated can flow, from a connecting chamber in which the power current is passed for the electrical supply of the PTC heating elements.
However, the present invention is not restricted to electrical heating devices of this nature normally designed for liquid media. Also an electrical heating device for heating air, in particular for heating the interior of a motor vehicle, can be regarded as generic. With this device the heating ribs are normally formed by meander-type bent sheet metal strips, which are exposed to the air flow to be heated and directly abut the PTC heating elements. These PTC heating elements comprise at least one PTC block and on oppositely situated sides of them abutting sheet metal bands, through which the PTC blocks can be supplied with electrical current with different polarity. The housing is normally formed by a frame, frequently of plastic. This frame has a very slight extension in the flow direction of the air to be heated. A generic electrical heating device of this nature with a control device in a constructional unit is for example known from EP 0 901 311 or DE 199 25 757.
Electrical heating devices of this nature switch high currents. With the usual on-board electrical voltage of 12 volts currents of over 250 amps and with high-voltage applications of 180 to 500 volts currents of over 70 amps are switched in order to obtain the required heating powers. This demands amongst other aspects special contacting of all elements of the electrical heating devices. A good contact resistance must always be ensured on all live connections. Furthermore, with electrical heating devices of this nature there is the problem that switching high currents leads to electromagnetic interference, which admittedly can be reduced with electrical heating devices with a control device in a constructional unit, but not completely eliminated. Thus, EMC problems continue to present an obstacle to a satisfactory electrical heating device producing high thermal outputs.